The summer box office season will go off with a bang with the highly anticipated Avengers: Age of Ultron film. The film already has a slew of superheroes but director Joss Whedon said there could likely be more.

Marvel's Lorraine Cink interviewed Whedon this week. At the end of the interview she asked him one last question, "Will we be seeing Marvel characters who aren't yet in the preview photos? Are we going to be seeing other Marvel characters that we've seen in other film or other parts of the universe?"

Whedon simply replied, "Yes."

Fans are now avidly theorizing just who could be appearing in the already heavily casted film. Some speculate that it could be a superhero that will have their own film in the upcoming years such as Black Panther, Ant-Man and Spider-Man. One fan, El Mayimbe from The Latino Review believes he already figured that heroine Captain Marvel will be the secret cast member.

Avengers: Age of Ultron already has twelve heroes: Captain America (Chris Evans), Thor (Chris Hemsworth), Iron Man (Robert Downey Jr.), The Hulk (Mark Ruffalo), Hawkeye (Jeremy Renner), Black Widow (Scarlett Johansson), Maria Hill (Cobie Smulders), War Machine (Don Cheadle), The Vision (Paul Bettany), and Nick Fury (Samuel L. Jackson). The two newcomers are Quicksilver (Aaron Taylor-Johnson) and the Scarlett Witch (Elizabeth Olsen).

Also making a brief appearance are Captain Falcon (Anthony Mackie) and Peggy Carter (Hayley Atwell).

Whedon said in the interview with Cink of Quicksilver and Scarlet Witch, "It was really important for me to have people who would change the game, emotionally and stylistically. Their powers are completely different [from the existing Avengers] and, through them, we get to see things differently."

Avengers: Age of Ultron releases in theaters on May 1.